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Re: Class.newInstance() question

daemon@ATHENA.MIT.EDU (Chuck McManis)
Thu Jul 13 03:04:55 1995

Date: Wed, 12 Jul 1995 22:43:14 -0700
From: cmcmanis@scndprsn.Eng.Sun.COM (Chuck McManis)
To: Anselm.Baird_Smith@inria.fr, java-interest@java.Eng.Sun.COM


The best way to do this is to define an interface that objects you want
to create this way can use. Thus you would define:

public interface Loadable {
    public Object make(String parameter);
}

And then in objects you were instantiating you would use:

    Class foo = Class.forName("MyCustomClass");
    return ((Loadable)(foo.newInstance()).make("Some parameter"));

Now you could also protect it like this:

    Object x;
 
    try {
	x = (Loadable) (foo.newInstance()).make("Some Parameter");
    } catch (Exception e) {
	// didn't work , probably doesn't implement loadable
	x = null;
    }
    return (x);

So if the object you were instantiating couldn't be made loadable it wouldn't.

You would write a loadable object like so:

class Bletch implements Loadable {
    /** MUST have a null constructor if you want newInstance to work */
    public Bletch(){
    }

    public Bletch(String xyzzy) {
    }

    public Bletch make(String fooey) {
	return new Bletch(fooey);
    }
}


A bit of overhead but it gets the job done. 

--Chuck
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